Results: Four strains (termed Sv29, Sv5, Sv26 and Sv30) contained the cpsA fragment. Sv29 contained licA and SV29 plus Sv5 contained comC. API20, PCR identification based on the species-specific D-Ala:D-Ala ligase gene (Garnier, JCM 1997, 35, 2337), whole cell protein profiling, high-resolution genotyping (AFLP) and sequence analysis of the 16S rRNA gene confirmed that Sv5, Sv26, Sv29, and Sv30 clustered in a single group and belonged to the S. mitis group. It is not clear whether they belong to a known species or constitute a new species within the S. mitis group.

Strain Sv29 was sequenced up- and downstream of cpsA. Approximately 25 kb of DNA (9 kb upstream of the cpsA start and 15 kb downstream) were comprised between an upstream dexB and a downstream aliA gene. 14 genes were found between the cpsA start and the aliA stop, comprising genes identical to the pneumococcal capsulation genes wzg (capsular polysaccharide expression regulator), wzh (Wze phosphotyrosine phosphatase), wzd (Wze phosphorylation), wze (autophosphorylating protein-tyrosine kinase), wchA (undecaprenyl phosphate glucose-phosphotransferase), wzy (oligosaccharide repeat unit polymerase), wzx (flippase) and several genes with putative glycosyl, glycerol and acetyl transferase activity and a putative UDP-galactopyranose mutase. Four genes were upstream between the cpsA start and the dexB start, comprising dexB, aliA-like orf1 and 2 genes and an unidentified gene. Expression of the capsulation locus genes was demonstrated. A Quellung reaction with multivalent antiserum to detect capsular polysaccharides remained negative in Sv29 and in Sv5, 26 and 30.

Conclusion: We report for the first time the presence of a pneumococcal-like capsulation locus in S. mitis group streptococci that are not S. pneumoniae. These genes may represent a new an unknown source of capsule variation in S. pneumoniae